<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=
    
    , initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <div id="app">

        <ul>
            <li>西游记;价格;{{xyjPrice}},数量：<input type="number" v-model="xyjNum"></li>
            <li>水浒传;价格;{{shzPrice}},数量：<input type="number" v-model="shzNum"></li>
            <li>总价;{{totalPrice}}</li>
        </ul>
        {{msg}}
    </div>

</body>

<script src="../node_modules/vue/dist/vue.js"></script>

<script>
    let vm = new Vue({
        el: "#app",
        data: {
            xyjPrice: 99,
            shzPrice: 95,
            xyjNum: 1,
            shzNum: 1,
            msg: ""
        },
        //计算属性存放
        computed: {
            totalPrice() {
                return this.xyjPrice * this.xyjNum + this.shzPrice * this.shzNum
            }
        },
        //对属性的监听    
        watch: {
            xyjNum: function (newVal, oldVal) {
                if (newVal >= 3) {
                    this.msg = "库存超出限制";
                    this.xyjNum = 3;
                }else{
                    this.msg = "";    
                }

            }
        }

    });



</script>

</html>